[R] SVM linear kernel and SV

From: David Meyer <david.meyer_at_wu-wien.ac.at>
Date: Fri 13 May 2005 - 21:04:43 EST


> Thank you for your answer,
> but my problem concerns the support vectors. Indeed the two classes
> are well separated and the hyperplane is linear but the support
> vectors aren't aligned in parallel to the hyperplane. And according to
> me, the support vectors (for each class) should be aligned along the
> linear hyperplane and form the marge (by definition). But it's not the
> case. In fact, I'd like to understand why they are not aligned.

Remember the `cost'-penalty controlling for overlapping classes. It has some effect even in the linearly separable case causing more SVs than would actually be needed. Try adding e.g. `cost=1000' and you will obtain a result with only 2 SVs (why not 3? Because 2 SVs here solve the optimization problem. So in fact the hyperplane in this case is not uniquely defined, although only in a small range.)

Best,

David



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